Gut bacteria implicated in a spectrum of important neurological pathologies

Tanvi Ambulkar, 15 Sep 2017

The composition of gut microbiota is critical not only for regulating the immune system, but also for maintaining mental health and combating extrinsic pathogens.

The human microbiota has always been at the heart of a range of medical conditions due to its important functions. Bacteria in the gut are responsible for absorption of essential vitamins, preventing growth of pathological microorganisms and even generating an environment that is conducive for digestion and absorption of nutrients.

Studies show link between gut flora and multiple sclerosis

Multiple sclerosis (MS) is a neurological condition where destruction of the myelin sheath responsible for insulating neurons occurs. The clinical presentation of multiple sclerosis comprises of symptoms, such as muscle spasms, impaired vision, pain and paresthesia.

In patients with multiple sclerosis, certain types of gut bacteria are more prevalent in comparison to the normal population. These gut bacteria are found to elevate the numbers of T helper cells, which are responsible for destruction of foreign organisms. In addition, regulatory T cells, which typically prevent the autoimmune destruction of normal tissues, are found to be reduced in these patients.

In particular, bacterial species Akkermansia and Acinetobacter are significantly raised in individuals who suffer from MS (four times more than individual with no disease). Both these species prompt inflammatory responses in the body, which can result in destruction of perceived target tissues. Another type of bacteria, Parabacteroides distasonis, which is responsible for modulating the immune responses of the body, is found at abysmally low levels in MS patients.

The roots of anxiety may lie in gut health

Consumption of probiotics in the form of yogurt and other dairy products have been purported as ways to enhance mental health. The scientific basis for this has now been established by a study published in the Microbiome journal, which states that microRNA (miRNA) molecules present in the brain can be influenced by the presence of certain gut microbes.

Gerard Clarke, MD, the lead researcher, comments on the specifics of this finding stating that: “Gut microbes seem to influence miRNAs in the amygdala and the prefrontal cortex.” These microRNA molecules are integral to the normal functioning of the central nervous system. The amygdala and prefrontal cortex are also routinely implicated in mental health conditions such as depression and anxiety, and therefore targeted treatment centred on these miRNA molecules may offer curative benefit for patients with these conditions.

Experimental mice included in the study that were devoid of a healthy microbiome were found not only to develop anxiety and depression, but also reduced cognitive ability and social skill. Dr Clarke underscores the magnificent scope of such research findings by stating that: “This is early stage research, but the possibility of achieving the desired impact on miRNAs in specific brain regions by targeting the gut microbiota – for example by using psychobiotics – is an appealing prospect.”

A different array of gut bacteria in individuals with Parkinson’s disease

Patients with Parkinson’s disease are found to possess different gut bacteria when compared to healthy individuals. Certain types of bacteria such as Akkermansia were found to be more prevalent in individuals with Parkinson’s whilst other bacterial species were present in fewer numbers.

Symptoms commonly encountered in Parkinson’s were also attributed to the presence of different types of bacteria. For instance, Anaerotruncus species differ widely between healthy individuals and Parkinson’s patients. Depression, which is frequently associated with Parkinson’s disease, is attributed to the difference in this type of bacteria.

This research finding is beneficial because it suggests that significantly altered microbiomes may have prognostic value. Patients who have an early stage of Parkinson’s disease are still found to have radically different microbiomes from their healthy counterparts. Although Parkinson’s is stipulated to originate from the invasion of a foreign pathogen via the nose or the gastrointestinal tract, nasal microbiomes were not found to be sufficiently different in patients with Parkinson’s disease. MIMS

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